Nonvolatile memory and erasing method thereof

ABSTRACT

An erase method of a nonvolatile memory includes supplying an erase voltage to a substrate, supplying a selection word line voltage to word lines connected with a selected sub-block within a memory block of the nonvolatile memory, supplying a non-selection word line voltage to word lines connected with an unselected sub-block within the memory block during a first delay time from a point of time when the erase voltage is supplied, and thereafter floating the word lines connected with the unselected sub-block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of application Ser. No. 14/644,247, filed Mar. 11,2015, which is a Continuation of application Ser. No. 14/485,049, filedSep. 12, 2014, which issued as U.S. Pat. No. 8,982,642, on Mar. 17,2015, and which is a Divisional of application Ser. No. 13/597,534,filed Aug. 29, 2012, which issued as U.S. Pat. No. 8,837,228, and inwhich a claim of priority under 35 U.S.C §119 is made to Korean PatentApplication No. 10-2011-0099914 filed Sep. 30, 2011, the entirety ofwhich is incorporated by reference herein.

BACKGROUND

Embodiments relate to a semiconductor memory device, and moreparticularly, to a memory system including a nonvolatile memory.

A semiconductor memory device is a memory device which is fabricated atleast partially from semiconductors such as silicon (Si), germanium(Ge), gallium arsenide (GaAs), indium phosphide (InP), and the like.Semiconductor memory devices are generally categorized as eithervolatile memory devices or nonvolatile memory devices.

The volatile memory devices are usually characterized by the loss ofstored data when power is interrupted or otherwise disconnected.Examples of volatile memory devices include certain types of randomaccess memory (RAM) such as static RAM (SRAM), dynamic RAM (DRAM),synchronous DRAM (SDRAM), and the like. The nonvolatile memory devicesmay retain stored contents even at power-off. Nonvolatile memorydevices, on the other hand, are usually characterized by the retentionof stored data when power is interrupted. Examples of nonvolatile memoryinclude read only memory (ROM), programmable ROM (PROM), electricallyprogrammable ROM (EPROM), electrically erasable and programmable ROM(EEPROM), flash memory device (e.g., NAND type and NOR type),phase-change RAM (PRAM), magnetic RAM (MRAM), resistive RAM (RRAM),ferroelectric RAM (FRAM), and the like.

Typically, the memory cell array of a semiconductor memory deviceextends in two dimensions with memory cells located at intersecting rowsand columns. Recently, however, semiconductor memory devices having athree-dimensional array structure have been developed to enhanceintegration densities.

SUMMARY

One aspect of embodiments of the inventive concept is directed toprovide an erase method of a nonvolatile memory which includes asubstrate and a memory block, the memory block having a plurality ofsub-blocks stacked on the substrate. The erase method includes supplyingan erase voltage to the substrate, supplying a selection word linevoltage to word lines connected with a selected sub-block within thememory block, and, after supplying a non-selection word line voltage toword lines connected with an unselected sub-block within the memoryblock during a first delay time from a point of time when the erasevoltage is supplied, floating the word lines connected with theunselected sub-block.

In this embodiment, the unselected sub-block may be placed between theselected sub-block and the substrate.

In this embodiment, the at least one memory block may further includedummy memory cells connected with a dummy word line. The erase methodmay further include, after supplying a dummy word line voltage to thedummy word line during a second delay time from a point of time when theerase voltage is supplied, floating the dummy word line.

In this embodiment, the dummy memory cells may be disposed to be closerto the substrate than the selected sub-block and the unselectedsub-block, and the second delay time is shorter than the first delaytime.

In this embodiment, the dummy memory cells may be disposed to be closerto the substrate than the selected sub-block and the unselectedsub-block, and the memory block may further include ground selectiontransistors which are disposed between the dummy memory cells and thesubstrate and are connected to a ground selection line. The erase methodmay further include, after supplying a ground selection line voltage tothe ground selection line during a third delay time from a point of timewhen the erase voltage is supplied, floating the ground selection line.

In this embodiment, the third delay time may be shorter than the seconddelay time, and the second delay time is shorter than the first delaytime.

In this embodiment, the first through third times may be times taken forthe erase voltage to reach corresponding specific levels, respectively.

In this embodiment, the unselected sub-block may be disposed between theselected sub-block and the substrate, and the at least one memory blockmay further include a second unselected sub-block located farther fromthe substrate than the selected sub-block.

In this embodiment, the erase method may further include floating wordlines connected with the second unselected sub-block when the erasevoltage is supplied.

In this embodiment, the erase method may further include, aftersupplying the non-selection word line voltage to word lines connectedwith the second unselected sub-block during a second delay time from apoint of time when the erase voltage is supplied, floating the wordlines connected with the second unselected sub-block.

In this embodiment, the erase method may further include floating onesof word lines connected with the second unselected sub-block when theerase voltage is supplied, and, after supplying the non-selection wordline voltage to the others of the word lines connected with the secondunselected sub-block during a second delay time, floating the others ofthe word lines.

In this embodiment, the at least one memory block may further includestring selection transistors which are connected with a string selectionline and are placed to be far from the substrate than the plurality ofsub-blocks. The erase method may further include, after supplying astring selection line voltage to the string selection line during asecond delay time from a point of time when the erase voltage issupplied, floating the string selection line.

Another aspect of embodiments of the inventive concept is directed toprovide a nonvolatile memory including a memory cell array including asubstrate and a memory block, the memory block having a plurality ofsub-blocks stacked on the substrate. The nonvolatile memory furtherincludes an address decoder connected with the memory cell array via aplurality of word lines, and a voltage generator configured to generatean erase voltage. The address decoder is configured to float word linesconnected with an unselected sub-block of the memory block, aftersupplying a non-selection word line voltage to the word lines connectedwith the unselected sub-block until a delay time elapses from a point oftime when the erase voltage is supplied.

In this embodiment, the address decoder may be further configured tosupply a selection word line voltage to word lines connected with aselected sub-block of the memory block when the erase voltage issupplied.

In this embodiment, the unselected sub-block may be located between theselected sub-block and the substrate.

Another aspect of embodiments of the inventive concept is directed toprovide a nonvolatile memory which includes a three-dimensional (3D)memory cell array. The 3D memory cell array includes a substrate and amemory block, the memory block including an array of memory cell stringsextending vertically over the substrate. The memory block includes firstand second sub-blocks stacked over the substrate such that the firstsub-block includes a first sub-set of memory cells of each memory cellstring and the second sub-block includes a second sub-set of memorycells of each memory cell string. The nonvolatile memory furtherincludes an address decoder connected with the memory cell array via aplurality of word lines, and a voltage generator configured to generatean erase voltage supplied to the substrate during an erase operation ofa selected sub-block among the first and second sub-blocks. The addressdecoder is configured to supply a selection word line voltage to wordlines connected with the selected sub-block among the first and secondsub-blocks, to supply a non-selection word line voltage to word linesconnected with an unselected sub-block among the first and secondsub-blocks during a first delay time from a point of time when the erasevoltage is supplied, and to float the word lines connected with theunselected sub-block after supplying the non-selection word linevoltage.

In this embodiment, the first sub-block may be located between thesubstrate and the second sub-block, and the first sub-block may be theunselected sub-block and the second sub-block may be the selectedsub-block.

In this embodiment, each memory cell string may include a stringselection transistor connected between a bit line and the memory cellsof the memory cell string, a ground selection transistor connected to acommon source line, and a dummy memory cell connected between groundselection transistor and the memory cells of the memory cell string.

In this embodiment, the address decoder may be further configured tosupply a dummy word line voltage to a dummy word line of the dummymemory cell during a second delay time from a point of time when theerase voltage is supplied, and to float the dummy word line aftersupplying the dummy word line voltage, where the second delay time isshorter than the first delay time.

In this embodiment, the address decoder may be further configured tosupply a ground selection line voltage to the ground selection lineduring a third delay time from a point of time when the erase voltage issupplied, and to float the ground selection line after supplying theground selection line voltage, where the third delay time is shorterthan the second delay time.

BRIEF DESCRIPTION OF THE FIGURES

The above and other objects and features will become apparent from thedetailed description that follows with reference to the accompanyingfigures, wherein like reference numerals refer to like parts throughoutthe various figures unless otherwise specified.

FIG. 1 is a block diagram schematically illustrating a nonvolatilememory according to an embodiment of the inventive concept.

FIG. 2 is a diagram schematically illustrating a memory cell array inFIG. 1 according to an embodiment of the inventive concept.

FIG. 3 is a detailed block diagram illustrating memory blocks of FIG. 2.

FIG. 4 is a perspective view of a part of a memory block according to anembodiment of the inventive concept.

FIG. 5 is a cross-sectional view taken along a line V-V′ of FIG. 5.

FIG. 6 is a cross-sectional view of a transistor structure in FIG. 5.

FIG. 7 is an equivalent circuit diagram of a part of a memory block.

FIG. 8 is a circuit diagram illustrating an embodiment in which memorycells of an equivalent circuit in FIG. 7 are included in two sub-blocks.

FIG. 9 is a diagram illustrating one NAND string supplied with aplurality of voltages at an erase operation.

FIG. 10 is a table showing a bias condition in the event that memorycells of a memory block are included within two sub-blocks.

FIG. 11 is a timing diagram illustrating an embodiment of a voltagevariation of a memory block according to a bias condition of FIG. 10.

FIG. 12 is a flowchart for describing a method of controlling word linesconnected with an unselected sub-block at an erase operation.

FIG. 13 is a timing diagram illustrating another embodiment of a voltagevariation of a memory block according to a bias condition of FIG. 10.

FIG. 14 is a block diagram schematically illustrating a nonvolatilememory according to another embodiment of the inventive concept.

FIG. 15 is a timing diagram illustrating still another embodiment of avoltage variation of a memory block according to a bias condition ofFIG. 10.

FIG. 16 is a block diagram schematically illustrating a nonvolatilememory according to still another embodiment of the inventive concept.

FIG. 17 is a diagram illustrating an embodiment in which memory cells ofone NAND string are included within three sub-blocks.

FIG. 18 is a table illustrating an embodiment of a bias condition in theevent that memory cells of a memory block are included within threesub-blocks.

FIG. 19 is a timing diagram illustrating a voltage variation of a memoryblock according to a bias condition of FIG. 18.

FIG. 20 is a table illustrating another embodiment of a bias conditionin the event that memory cells of a memory block are included withinthree sub-blocks.

FIG. 21 is a table illustrating still another embodiment of a biascondition in the event that memory cells of a memory block are includedwithin three sub-blocks.

FIG. 22 is a table illustrating still another embodiment of a biascondition in the event that memory cells of a memory block are includedwithin three sub-blocks.

FIG. 23 is a circuit diagram illustrating an equivalent circuit of oneof memory blocks according to another embodiment of the inventiveconcept.

FIG. 24 is a table illustrating a bias condition on an equivalentcircuit of FIG. 23 when a first sub-block is unselected and a secondsub-block is selected.

FIG. 25 is a table illustrating a bias condition on an equivalentcircuit of FIG. 23 when a first sub-block is selected and a secondsub-block is unselected.

FIG. 26 is a block diagram illustrating a memory system according to anembodiment of the inventive concept.

FIG. 27 is a block diagram illustrating an application of a memorysystem in FIG. 26.

FIG. 28 is a block diagram illustrating a computing system including amemory system described in FIG. 27.

DETAILED DESCRIPTION

The inventive concept is described more fully hereinafter with referenceto the accompanying drawings, in which embodiments of the inventiveconcept are shown. This inventive concept may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the inventive concept to those skilled in the art.In the drawings, the size and relative sizes of layers and regions maybe exaggerated for clarity. Like numbers refer to like elementsthroughout.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the inventive concept.

Spatially relative terms, such as “beneath”, “below”, “lower”, “under”,“above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that the spatially relative terms are intended to encompassdifferent orientations of the device in use or operation in addition tothe orientation depicted in the figures. For example, if the device inthe figures is turned over, elements described as “below” or “beneath”or “under” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary terms “below” and“under” can encompass both an orientation of above and below. The devicemay be otherwise oriented (rotated 90 degrees or at other orientations)and the spatially relative descriptors used herein interpretedaccordingly. In addition, it will also be understood that when a layeris referred to as being “between” two layers, it can be the only layerbetween the two layers, or one or more intervening layers may also bepresent.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to”, “coupled to”, or “adjacent to” anotherelement or layer, it can be directly on, connected, coupled, or adjacentto the other element or layer, or intervening elements or layers may bepresent. In contrast, when an element is referred to as being “directlyon,” “directly connected to”, “directly coupled to”, or “immediatelyadjacent to” another element or layer, there are no intervening elementsor layers present.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this inventive concept belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and/orthe present specification and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

FIG. 1 is a block diagram schematically illustrating a nonvolatilememory according to an embodiment of the inventive concept. Referring toFIG. 1, a nonvolatile memory 100 of this example includes a memory cellarray 110, an address decoder 120, a voltage generator 130, a read andwrite circuit 140, and control logic 150.

The memory cell array 110 may be connected to the address decoder 120.The memory cell array 110 may be connected to the read and write circuit140 via bit lines BL. The memory cell array 110 may include a pluralityof memory cells. The memory cells may be stacked on a substrate. Each ofthe memory cells may store one or more bits of data.

The address decoder 120 may be connected to the memory cell array 110via a plurality of lines (e.g., string selection lines, word lines, andground selection lines). The address decoder 120 may be connected to thevoltage generator 130. The address decoder 120 may operate responsive tothe control of the control logic 150.

The address decoder 120 may receive an address ADDR from an externaldevice.

The address decoder 120 may decode a row address of the input addressADDR. The address decoder 120 may select a word line corresponding tothe decoded row address. The address decoder 120 may select a word linecorresponding to the input address ADDR by applying voltages, providedfrom the voltage generator 130, to the plurality of lines according tothe decoded row address.

At an erase operation, the address decoder 120 may apply voltages fromthe voltage generator 130 to some of the plurality of lines and mayfloat the remaining of the plurality of lines. Points of time in whichthe remaining lines are floated may be controlled by the control logic150, respectively. For example, a selection word line voltage may beapplied to selected word lines, and unselected word lines may be floatedafter an erase voltage is supplied to a substrate of the memory cellarray 110 and a specific delay time elapses.

The address decoder 120 may decode a column address of the input addressADDR. The address decoder 120 may provide the decoded column address tothe read and write circuit 140.

In an embodiment, the address decoder 120 may include a row decoderdecoding a row address, a column decoder decoding a column address, andan address buffer storing an address ADDR.

The voltage generator 130 may be connected to the control logic 150 andthe address decoder 120. The voltage generator 130 may operateresponsive to the control of the control logic 150. The voltagegenerator 130 may be configured to generate a high voltage. For example,voltages generated by the voltage generator 130 may be transferred tothe plurality of lines of the memory cell array 110 via the addressdecoder 120. A voltage generated by the voltage generator 130 may besupplied to the substrate of the memory cell array 110.

The read and write circuit 140 may be connected to the memory cell array110 via the bit lines BL. The read and write circuit 140 may operateresponsive to the control of the control logic 150. The read and writecircuit 140 may receive the decoded column address from the addressdecoder 120. The read and write circuit 140 may select the bit lines BLusing the decoded column address.

In an embodiment, at a program operation, the read and write circuit 140may program data provided from external the memory cell array 110. At aread operation, the read and write circuit 140 may read data from thememory cell array 110 for external transfer. The read and write circuit140 may read data from a first storage region of the memory cell array110 to write it in a second storage region of the memory cell array 110.For example, the read and write circuit 140 may perform a copy-backoperation.

In an embodiment, the read and write circuit 140 may include constituentelements such as a page buffer (or, a page register), a column selector,and the like. In another embodiment, the read and write circuit 140 mayinclude constituent elements such as a sense amplifier, a write driver,a column selector, and the like.

In an embodiment, although not shown in FIG. 1, the nonvolatile memory100 may further comprise a constituent element such as a buffer circuit.In this case, the buffer circuit may receive externally supplied programdata at a program operation, and may externally transfer read data at aread operation. The read and write circuit 140 may receive data from thebuffer circuit at a program operation, and may transfer data read fromthe memory cell array 110 to the buffer circuit.

The control logic 150 may be connected to the address decoder 120, thevoltage generator 130, and the read and write circuit 140. The controllogic 150 may be configured to control an overall operation of thenonvolatile memory 100. The control logic 150 may operate responsive toa control signal CTRL from the outside.

At an erase operation, the control logic 150 may control the voltagegenerator 130 such that an erase voltage generated from the voltagegenerator 130 is transferred to the substrate of the memory cell array110. With the inventive concept, the control logic 150 may adjust apoint of time when unselected word lines are floated at an eraseoperation. For example, the control logic 150 may control the addressdecoder 120 such that unselected word lines are floated after a specificdelay time elapses from a point of time when an erase voltage issupplied to the substrate of the memory cell array 110.

FIG. 2 is a diagram schematically illustrating a memory cell array inFIG. 1 according to an embodiment of the inventive concept. Referring toFIG. 2, a memory cell array 110 may include a plurality of memory blocksBLK1 through BLKz, each of which is formed to have a three-dimensionalstructure (or, a vertical structure). For example, each of the memoryblocks BLK1 through BLKz may include structures extending along first tothird directions. Although not shown in FIG. 2, each of the memoryblocks BLK1 through BLKz may include a plurality of cell stringsextending along the second direction. For example, a plurality of NANDstrings NS may be provided along the first and third directions.

Each memory block may be connected to a plurality of bit lines BL, aplurality of string selection lines, a plurality of ground selectionlines, and a common source line. Each NAND string NS may be connected toa bit line, a string selection line, a ground selection line, wordlines, and a common source line. Each memory block will be more fullydescribed later with reference to FIG. 4.

The plurality of memory blocks BLK1 through BLKz may be selected by anaddress decoder 120 in FIG. 1. For example, the address decoder 120 maybe configured to select a memory block, corresponding to a decoded rowaddress, from among the plurality of memory blocks BLK1 to BLKz.

FIG. 3 is a detailed block diagram illustrating memory blocks BLK1through BLKz of FIG. 2. In FIG. 3, for ease of illustration, a firstmemory block BLK1 is illustrated in detail. However, like the firstmemory block BLK1, the remaining memory blocks BLK2 through BLKz may beconfigured the same as illustrated in FIG. 3.

Referring to FIG. 3, the memory block BLK1 may include a plurality ofNAND strings. One NAND string may include a ground selection transistorGST, a dummy memory cell DMC, first through sixth memory cells MC1through MC6, and a string selection transistor SST.

The memory block BLK1 may be connected to bit lines BL1 through BLm. Thememory block BLK1 may be connected to string selection lines SSL1through SSLn, first through sixth word lines WL1 through WL6, a dummyword line DWL, a ground selection line GSL, and a common source lineCSL.

A gate (or, a control gate) of a string selection transistor SST may beconnected to a string selection line SSL1 and between a bit line and thesixth memory cell MC6.

The first through sixth memory cells MC1 through MC6 may be connected inseries, and may be connected to the string selection transistor SST anda dummy memory cell DMC. Gates (or, control gates) of the first throughsixth memory cells MC1 through MC6 may be connected to first throughsixth word lines WL1 through WL6, respectively.

The dummy memory cell DMC may be connected to the first memory cell MC1and a ground selection transistor GST. A gate (or, a control gate) ofthe dummy memory cell DMC may be connected to the dummy word line DWL.The ground selection transistor GST may be connected between the dummymemory cell DMC and the common source line CSL. A gate (or, a controlgate) of the ground selection transistor GST may be connected to theground selection line GSL.

The memory cell array 110 illustrated in FIG. 3 is an example only, andthe inventive concept is not limited thereto. As one variation, forexample, one NAND string can be configured to include 7 or more memorycells and to include two or more dummy memory cells.

FIG. 4 is a perspective view of a part of a memory block BLK1 accordingto an embodiment of the inventive concept, and FIG. 5 is across-sectional view taken along a line V-V′ of FIG. 5. Referring toFIGS. 4 and 5, a part BLK1 a of a memory block BLK1 may includestructures that extend along first to third directions.

First, a substrate 111 may be provided. Exemplarily, the substrate 111may be a well of a first type (e.g., a first conductive type). Forexample, the substrate 111 may be a p-well in which a Group III elementsuch as boron is injected. For example, the substrate 111 may be apocket p-well which is provided within an n-well. Below, it is assumedthat the substrate 111 is a p-well (or, a pocket p-well). However, thesubstrate 111 is not limited thereto.

A plurality of doping regions 311 through 314 extending along the firstdirection may be provided at the substrate 111. For example, a pluralityof doping regions 311 through 314 may have a second type different fromthe substrate 111. For example, the doping regions 311 through 314 maybe an n-type. Hereinafter, it is assumed that the first through fourthdoping regions 311 through 314 are an n-type. However, the first throughfourth doping regions 311 through 314 are not limited thereto.

On the substrate 111 between the first and second doping regions 311 and312, a plurality of insulating materials 112 and 112 a extending alongthe first direction may be sequentially provided along the seconddirection. For example, the insulating materials 112 and 112 a mayinclude an insulating material such as silicon oxide. For example, athickness of an insulating material 112 a contacting with the substrate111 may be thinner than those of the remaining insulating materials 112.For example, the plurality of insulating materials 112 may be formed tobe separated by a predetermined distance along the second direction.

On the substrate 111 between the first and second doping regions 311 and312, a plurality of pillars 113 may be provided which are sequentiallydisposed along the first direction and pass through the insulatingmaterials 112 along the second direction. Exemplarily, the pillars 113may contact the substrate 111 through the insulating materials 112,respectively.

Exemplarily, each of the pillars 113 may be formed of a plurality ofmaterials. For example, a surface layer 114 of each pillar 113 mayinclude a silicon material having the first type. For example, thesurface layer 114 of each pillar 113 may include a silicon materialhaving the same type as the substrate 111. Hereinafter, it is assumedthat the surface layer 114 of each pillar 113 includes p-type silicon.However, the surface layer 114 of each pillar 113 is not limitedthereto.

An inner layer 115 of each pillar 113 may be formed of an insulatingmaterial. For example, the inner layer 115 of each pillar 113 mayinclude an insulating material such as silicon oxide. For example, theinner layer 115 of each pillar 113 can include an air gap.

Between the first and second doping regions 311 and 312, an insulatingfilm 116 may be provided along exposed surfaces of the substrate 11, theinsulating materials 112, and the pillars 113. For example, thethickness of the insulating film 116 may be less than half a distancebetween the insulating materials 112. That is, a region where a materialother than the insulating materials 112 and the insulation layer 116 isdisposed may be provided between an insulating film 116 provided on alower surface of a first insulating material among the insulatingmaterials 112 and an insulating film 116 provided on an upper surface ofa second insulating material and at the lower portion of the firstinsulating material.

Between the first and second doping regions 311 and 312, firstconductive materials 211 through 291 may be provided on an exposedsurface of the insulating film 116. For example, the first conductivematerial 211 extending along the first direction may be provided betweenthe substrate 111 and the insulating material 112 adjacent to thesubstrate 111. A plurality of first conductive materials 221 through 281extending along the first direction may be provided among the insulatingmaterials 112. For example, the first conductive materials 211 through291 may be a metal material. For example, the first conductive materials211 through 291 may be a conductive material.

The same structure as the first and second doping regions 311 and 312may be provided between the second and third doping regions 312 and 313.Between the second and third doping regions 312 and 313, exemplarily,there may be provided the insulating materials 112 extending along thefirst direction, the pillars 113 sequentially disposed in the firstdirection and passing through the insulating materials 112 along thesecond direction, the insulating film 116 exposed surfaces of thepillars 113 and the insulating materials 112, and the first conductivematerials 212 through 292 extending along the first direction.

The same structure as a structure on the first and second doping regions311 and 312 may be provided between the third and fourth doping regions313 and 314. Between the third and fourth doping regions 313 and 314,exemplarily, there may be provided the insulating materials 112extending along the first direction, the pillars 113 sequentiallydisposed in the first direction and passing through the insulatingmaterials 112 in the third direction, the insulation layer 116 theexposed surfaces of the insulating materials 112 and the pillars 113,and the first conductive materials 213 through 293 extending along thefirst direction.

Drains 320 may be provided on the pillars 113, respectively.Exemplarily, the drains 320 may include a silicon material that is dopedof a second type. For example, the drains 320 may be an n-type siliconmaterial. Hereinafter, it is assumed that the drains 320 include ann-type silicon material. However, the drains 320 are not limitedthereto.

Exemplarily, the width of each of the drains 320 may be wider than thatof a corresponding pillar 113. For example, each drain 320 may beprovided in a pad shape on the upper surface of a corresponding pillar113. Exemplarily, each drain 320 may be extended up to a part of thesurface layer 114 of a corresponding pillar 113.

Second conductive materials 331 through 333 extending along the thirddirection may be provided on the drains 320. The conductive materials331 through 333 may be spaced apart along the first direction. Theconductive materials 331 to 333 may be connected to the drains 320 ofcorresponding regions, respectively. Exemplarily, the drains 320 and thesecond conductive material 333 extending along the third direction maybe connected through contact plugs. Exemplarily, the second conductivematerials 331 through 333 may be a metal material. Exemplarily, thesecond conductive materials 331 through 333 may be a conductive materialsuch as polysilicon.

Below, heights of the first conductive materials 211 through 291, 212through 292, and 213 through 293 may be defined. The first conductivematerials 211 through 291, 212 through 292, and 213 through 293 may bedefined to have first through ninth heights sequentially from asubstrate 111. The first conductive materials 211 through 213 adjacentto the substrate 111 may have a first height. The first conductivematerials 291 through 293 adjacent to first conductive materials 331through 333 may have a ninth height. A height of each of the firstconductive materials 211 through 291, 212 through 292, and 213 through293 may increase in proportion to a distance from the substrate 111.

In FIGS. 4 and 5, each pillar 113 may form a string together with thefirst conductive materials 211 through 291, 212 through 292, and 213through 293. For example, each pillar 113 may form a NAND string NStogether with an adjacent region of an insulating film 116 and anadjacent region among the first conductive materials 211 through 291,212 through 292, and 213 through 293. The NAND string NS may include aplurality of transistor structures TS. The transistor structure TS willbe more fully described with reference to FIG. 6.

FIG. 6 is a cross-sectional view of a transistor structure TS in FIG. 5.Referring to FIGS. 4 through 6, an insulating film 116 may include firstto third sub-insulating films 117 through 119.

A p-type silicon surface layer 114 of a pillar 113 may act as a body.The first sub-insulating film 117 may act as a tunneling insulatingfilm. For example, the first sub-insulating film 117 adjacent to thepillar 113 may include a thermal oxide layer.

The second sub-insulating film 118 may act as a charge storage film. Forexample, the second sub-insulating film 118 may act as a charge traplayer. For example, the second sub-insulating film 118 may include anitride layer or a metal oxide layer (e.g., an aluminum oxide layer, ahafnium oxide layer, or the like).

Exemplarily, the third sub-insulating film 119 adjacent to a firstconductive material 233 may act as a blocking insulating film. The thirdsub-insulating film 119 may be a high-k dielectric layer (e.g., analuminum oxide layer or a hafnium oxide layer) having a higherdielectric constant than the first and second sub-insulating films 117and 118 (e.g., silicon dioxide).

The first conductive material 233 may serve as a gate (or a controlgate). That is, the first conductive material 233 serving as a gate (ora control gate), the third sub-insulating film 119 serving as theblocking insulating film, the second sub-insulating film 118 serving asthe charge storage layer, the first sub-insulating film 117 serving asthe tunneling insulation layer, and the p-type surface layer 114 servingas a body may form a transistor (or, a memory cell transistorstructure). Exemplarily, the first through third sub-insulating films117 through 119 may form oxide-nitride-oxide (ONO). Below, it is assumedthat the p-type surface layer 114 of the pillar 113 serves as asecond-direction body.

In a part BLK1 a of a memory block BLK1, one pillar 113 may correspondto one NAND string NS. The part BLK1 a of a memory block BLK1 mayinclude a plurality of pillars 113. That is, the memory block BLK1 mayinclude a plurality of NAND strings NS.

Each NAND string NS may include a plurality of transistor structures TSthat are stacked along a second direction. At least one of thetransistor structures TS of each NAND string NS may serve as a stringselection transistor SST. At least one of the transistor structures TSof each NAND string NS may serve as a ground selection transistor GST.

Gates (or control gates) may correspond to the first conductivematerials 211 through 291, 212 through 292, and 213 through 293extending along the first direction. That is, the gates (or the controlgates) may be extended in the first direction to form string selectionlines SSL (refer to FIG. 7), word lines WL (refer to FIG. 7), at leastone dummy word line DWL (refer to FIG. 7), and at least one groundselection line GSL (refer to FIG. 7).

The second conductive materials 331 through 333 extending in the thirddirection may be connected to one ends of the NAND strings NS,respectively. The second conductive materials 331 through 333 may act asbit lines BL. In the memory block BLK1, one bit line may be connectedwith a plurality of NAND strings. Further, one bit line may be connectedwith NAND strings of the memory block BLK1 as well as NAND strings ofmemory blocks BLK2 through BLKz (refer to FIG. 3).

Second-type doping regions 311 through 314 extending in the firstdirection may be provided to other ends of the NAND strings NS,respectively. The second-type doping regions 311 through 314 may serveas a common source line CSL.

To sum up the above-described, the memory block BLK1 may include aplurality of NAND strings that are extended in a direction (i.e., thesecond direction) vertical to the substrate 111, and a plurality of NANDstrings NS may be connected to one bit line BL.

FIGS. 4 to 6 were described under the assumption first conductive lines211 through 291, 212 through 292, and 213 through 293 are formed at ninelayers. However, the inventive concept is not limited thereto. Forexample, first conductive materials can be formed on at least 8 or 16layers for memory cells and at least 2 layers for selection transistors.

An area (hereinafter, referred to as a cross-section area) of a pillar113 taken along first and third directions may be varied due to processcharacteristics or errors. As illustrated in FIGS. 4 through 6, thecloser to the substrate 111, the narrower the cross-sectional area. Thepillar 113 may be formed by filling a hole formed by etching withmaterials such as a silicon material and an insulating material. Thecross-sectional area of a hole formed by etching may decrease inproportion to an increase of an etched depth.

FIG. 7 is an equivalent circuit diagram of a part BLK1 a of a memoryblock BLK1. Referring to FIGS. 4 to 7, NAND strings NS11, NS21, and NS31may be provided between a first bit line BL1 and a common source lineCSL. NAND strings NS12, NS22, and NS32 may be provided between a secondbit line BL2 and the common source line CSL. NAND strings NS13, NS23,and NS33 may be provided between a third bit line BL3 and the commonsource line CSL. The first through third bit lines BL1 through BL3 maycorrespond to conductive material 331 through 333 extending in the thirddirection, respectively.

A string selection transistor SST of each NAND string NS may beconnected to a corresponding bit line BL. A ground selection transistorGST of each NAND string NS may be connected to the common source lineCSL. In each NAND string NS, memory cells MC may be provided between thestring selection transistor SST and the ground selection transistor GST.

Below, NAND strings NS may be defined by row and by column. The NANDstrings NS connected to one bit line in common may form one column. Forexample, the NAND strings NS11 through NS31 connected to the first bitline BL1 may correspond to a first column. The NAND strings NS12 throughNS32 connected to the second bit line BL2 may correspond to a secondcolumn. The NAND strings NS13 through NS33 connected to the third bitline BL3 may correspond to a third column.

The NAND strings NS connected to one string selection line SSL may formone row. For example, the NAND strings NS11 through NS13 connected to afirst string selection line SSL1 may form a first row. The NAND stringsNS21 through NS23 connected to a second string selection line SSL2 mayform a second row. The NAND strings NS31 through NS33 connected to athird string selection line SSL3 may form a third row.

In each NAND string NS, a nominal height (i.e., relative verticallocation) may be defined. Exemplarily, in each NAND string NS, theground selection transistor GST may be defined to have a nominal heightof 1. A dummy memory cell DMC adjacent to the ground selectiontransistor GST may be defined to have a nominal height of 2. A memorycell MC1 adjacent to the dummy memory cell DMC may be defined to have anominal height of 3. The string selection transistor SST may be definedto have a nominal height of 9. A memory cell MC6 adjacent to the stringselection transistor SST may be defined to have a nominal height of 8.

As a memory cell is far from the ground selection transistor GST, anominal height of a memory cell may increase. That is, first throughthird memory cells MC1 through MC3 may be defined to have third throughfifth nominal heights, respectively, and fourth through sixth memorycells MC4 through MC6 may be defined to have sixth through eight nominalheights, respectively.

The NAND strings NS11 through NS13, NS21 through NS23, and NS31 throughNS33 may share a ground selection line GSL. The first conductivematerials 211 through 213 having the first nominal height may beinterconnected to form the ground selection line GSL.

In each NAND string in the same row, memory cells having the samenominal height may share a word line WL. NAND strings having the samenominal height and corresponding to different rows may share a wordline. That is, memory cells having the same nominal height may share aword line WL.

The first conductive materials 221 through 223 having the second nominalheight may be interconnected to form a dummy word line DWL. The firstconductive materials 231 through 233 having the third nominal height maybe interconnected to form a first word line WL1. The first conductivematerials 241 through 243 having the fourth nominal height may beinterconnected to form a second word line WL2. The first conductivematerials 251 through 253 having the fifth nominal height may beinterconnected to form a third word line WL3. The first conductivematerials 261 through 263 having the sixth nominal height may beinterconnected to form a fourth word line WL4. The first conductivematerials 271 through 273 having the seventh nominal height may beinterconnected to form a fifth word line WL5. The first conductivematerials 281 through 283 having the eighth nominal height may beinterconnected to form a sixth word line WL6.

NAND strings in the same row may share the string selection line SSL.NAND strings in different rows may be connected to different stringselection lines SSL1, SSL2, and SSL3, respectively. The string selectionlines SSL1, SSL2, and SSL3 may correspond to first conductive materials291 through 293 having the ninth height, respectively.

The common source line CSL may be connected in common to NAND stringsNS. For example, first through fourth doping regions 311 through 314 maybe interconnected to form the common source line CSL. Further, thecommon source line CSL may be connected in common to NAND strings withina memory cell array 110 (refer to FIG. 3).

As illustrated in FIG. 7, word lines placed at the same nominal heightmay be connected in common Thus, when a word line placed at a specificnominal height is selected, all NAND strings connected with the selectedword line may be selected.

NAND strings in different rows may be connected to different stringselection lines. Thus, NAND strings in an unselected row from among NANDstrings connected with the same word line may be separated from acorresponding bit line and NAND strings in a selected row may beconnected to a corresponding bit line, by selecting and unselectingstring selection lines SSL1 through SSL3.

That is, a row of NAND strings may be selected by selecting andunselecting the string selection lines SSL1 through SSL3. This operationmay be executed by an address decoder 120 (refer to FIG. 1). A column ofNAND strings in a selected row may be selected by selecting bit linesBL1 through BL3.

In an embodiment, at program and read operations, one of the stringselection lines SSL1 through SSL3 may be selected. That is, the programand read operations may be executed by a row unit of NAND strings NS11through NS13, NS21 through NS23, and NS31 through NS33.

FIG. 8 is a circuit diagram illustrating an embodiment in which memorycells of an equivalent circuit in FIG. 7 are included in two sub-blocks.Referring to FIG. 8, a first sub-block may be formed of first throughthird memory cells MC1 through MC3. That is, memory cells placed atthird through fifth nominal heights may be included in the firstsub-block. A second sub-block may include fourth through sixth memorycells MC4 through MC6. Memory cells placed at sixth through eighthnominal heights may constitute the second sub-block.

An erase operation may be executed by a sub-block unit. Sub-blocks maybe erased independently. For example, when the first sub-block iserased, the second sub-block may be erase-inhibited. When the secondsub-block is erased, the first sub-block may be erase-inhibited. Thatis, in each NAND string, while some (e.g., MC1 through MC3) of memorycells MC1 through MC6 are erased, the remaining (e.g., MC4 through MC6)of the memory cells MC1 through MC6 may be erase-inhibited.

FIG. 9 is a diagram illustrating one NAND string supplied with aplurality of voltages at an erase operation. It is assumed that a secondsub-block is erased and a first sub-block is erase-inhibited.

Referring to FIGS. 8 and 9, at an erase operation, an erase voltage Versmay be supplied to a substrate 111. At this time, the erase voltage Versmay be a high voltage. A conduction type of the substrate 111 may beidentical to that of a surface layer 114 which acts as asecond-direction body.

A first conductive material 211 having a first nominal height may act asa ground selection line GSL, that is, a gate (or, a control gate) of aground selection transistor GST. The first conductive material 211 maybe floated. The conductive material 211 may be affected by the couplingfrom the substrate 111 and the surface layer 114. Thus, a voltage of thefirst conductive material 211 may be increased when a voltage of thesurface layer 114 rises to the erase voltage Vers. A difference betweenthe erase voltage Vers and the increased voltage of the first conductivematerial 211 may be insufficient to cause the Fowler-Nordheim tunneling.Accordingly, the ground selection transistor GST may be erase-inhibited.

A first conductive material 221 having a second nominal height may actas a dummy word line DWL and as a gate (or, a control gate) of a dummymemory cell DMC. The first conductive material 221 may be floated. Thus,the first conductive material 221 may be affected by coupling from thesurface layer 114. Thus, a voltage of the first conductive material 221may be increased when a voltage of the surface layer 114 rises to theerase voltage Vers. A difference between the erase voltage Vers and theincreased voltage of the first conductive material 221 may beinsufficient to cause the Fowler-Nordheim tunneling. Accordingly, thedummy memory cell DMC may be erase-inhibited.

First conductive materials 231 through 251 having third through fifthnominal heights may act as first through third word lines WL1 throughWL3 and as gates (or, control gates) of first through third memory cellsMC1 through MC3, respectively. The first conductive materials 231through 251 acting as unselected word lines may be floated. The firstconductive materials 231 through 251 may be affected by coupling fromthe surface layer 114. Thus, voltages of the first conductive materials231 through 251 may be increased when a voltage of the surface layer 114rises to the erase voltage Vers. A difference between the erase voltageVers and the increased voltages of the first conductive materials 231through 251 may be insufficient to cause the Fowler-Nordheim tunneling.Accordingly, the first through third memory cells MC1 through MC3 of afirst sub-block unselected may be erase-inhibited.

First conductive materials 261 through 281 having sixth through eighthnominal heights may act as fourth through sixth word lines WL4 throughWL6 and as gates (or, control gates) of fourth through sixth memorycells MC4 through MC6, respectively. The first conductive materials 261through 281 acting as selected word lines may be supplied with aselection word line voltage Vsw. For example, the selection word linevoltage Vsw may be a low voltage. A difference between the erase voltageVers of the surface layer 114 and the selection word line voltage Vswmay be sufficient to cause the Fowler-Nordheim tunneling. Accordingly,the fourth through sixth memory cells MC4 through MC6 of a secondsub-block may be erased.

A first conductive material 291 having a ninth nominal height may act asa string selection line SSL and as a gate (or, a control gate) of astring selection transistor SST. The string selection line SSL may befloated. The conductive material 291 may be affected by the couplingfrom the surface layer 114. Thus, a voltage of the first conductivematerial 291 may be increased when a voltage of the surface layer 114rises to the erase voltage Vers. A difference between the erase voltageVers and the increased voltage of the first conductive material 291 maybe insufficient to cause the Fowler-Nordheim tunneling. Accordingly, thestring selection transistor SST may be erase-inhibited.

The erase voltage Vers supplied to the substrate 111 may not betransferred stably to the surface layer 114. If the first conductivematerial 211 acting as the ground selection line GSL is floated, avoltage of the first conductive material 211 may be increased when theerase voltage Vers supplied to the substrate 111 is increased. Theincreased voltage of the first conductive material 211 may hinder theerase voltage Vers supplied to the substrate 111 from being stablytransferred to the surface layer 114.

For example, a transfer of the erase voltage Vers supplied to thesubstrate 111 may be understood as a transfer of a hole to the surfacelayer 114 from the substrate 111. An increase in a voltage of the firstconductive material 211 may hinder a hole from being transferred to thesurface layer 114 from the substrate 111. A voltage of the firstconductive material 221 acting as the dummy word line DWL and voltagesof the first conductive materials 231 through 251 acting as the firstthrough third word lines WL1 through WL3 may be increased by thecoupling effect. The increased voltages of the first conductivematerials 231 through 251 may also hinder a hole from being transferredto the surface layer 114 from the substrate 111.

In another example, if a voltage of the first conductive material 221 isincreased according to an increase in the erase voltage Vers supplied tothe substrate 111, a channel may be formed at a surface layercorresponding to the ground selection transistor GST. In this case, thesurface layer corresponding to the ground selection transistor GST maybe unintentionally changed into an n-type. This means that the erasevoltage Vers of the substrate 111 being a p-type is not transferredstably to the surface layer 114. Likewise, a channel may be formed at asurface layer corresponding to the dummy memory cell DMC and the firstthrough third memory cells MC1 through MC3 due to increased voltages ofthe first conductive materials 221 through 251. In this case, the erasevoltage Vers of the substrate 111 may not be transferred stably to thesurface layer 114.

In addition, the erase voltage Vers of the substrate 111 may not betransferred stably to the surface layer 114 due to various causes.

In the event that the erase voltage Vers of the substrate 111 is nottransferred stably to the surface layer 114, for example, a voltage ofthe surface layer 114 may be lower than the erase voltage Vers. Adifference between the voltage of the surface layer 114 and theselection word line voltage Vsw may be insufficient to generate theFowler-Nordheim tunneling. Accordingly, it is difficult to secure thereliability of the erase operation.

FIG. 10 is a table of a bias condition in the event that memory cells ofa memory block BLK1 are included within two sub-blocks. Referring toFIGS. 8 through 10, an erase voltage Vers may be supplied to a substrate111 at an erase operation.

A ground selection line GSL may be floated after a lapse of a specificdelay time from a point of time when the erase voltage Vers is supplied.After supplied with a ground selection line voltage Vgsl, the groundselection line GSL may be floated.

With the inventive concept, a dummy word line DWL may be floated afterthe erase voltage Vers is supplied and a specific delay time elapses.After being supplied with a dummy word line voltage Vdw, the dummy wordline DWL may be floated. After being supplied with a non-selection wordline voltage Vusw, word lines of an unselected sub-block may be floated.

In an embodiment, the ground selection line voltage Vgsl, the dummy wordline voltage Vdw, and the non-selection word line voltage Vusw may be alow voltage. For example, the ground selection line voltage Vgsl, thedummy word line voltage Vdw, and the non-selection word line voltageVusw may be a ground voltage Vss.

A selection word line voltage Vsw being a low voltage may be supplied toword lines of a selected sub-block. For example, the selection word linevoltage Vsw may be a ground voltage Vss. A string selection line SSL maybe floated.

With the inventive concept, the ground selection line GSL, the dummyword line, and the word lines of the unselected sub-block may be floatedafter the erase voltage Vers is supplied and a specific delay timeelapses. As low voltages are provided to the ground selection line GSL,the dummy word line, and the word lines of the unselected sub-blockbefore floated, the erase voltage Vers supplied to the substrate 111 maybe stably transferred to a surface layer 114. Thus, it is possible toimprove the reliability of an erase operation on memory cells of aselected sub-block.

FIG. 11 is a timing diagram illustrating an embodiment of a voltagevariation of a memory block BLK1 according to a bias condition of FIG.10. It is assumed that a second sub-block is a sub-block to be erased.That is, a first sub-block may be an unselected sub-block, and thesecond sub-block may be a selected sub-block.

Referring to FIGS. 9 through 11, at t1, an erase voltage Vers may startto be supplied to a substrate 111. The erase voltage Vers may be a highvoltage.

At the point of time t1 when the erase voltage Vers starts to beapplied, a ground selection line voltage Vgsl may be applied to a groundselection line GSL, a dummy word line voltage Vdw to a dummy word lineDWL, and a non-selection word line voltage Vusw to word lines WL1through WL3 of the first sub-block.

The ground selection line voltage Vgsl, the dummy word line voltage Vdw,and the non-selection word line voltage Vusw may be a low voltage. Adifference between each of the voltages Vgsl, Vdw, and Vusw and theerase voltage Vers may be maintained between t1 and t2. Thus, the erasevoltage Vers increasing may be stably transferred to a surface layer 114corresponding to memory cells MC4 through MC6 of the second sub-block.

At t1, a selection word line Vsw may be supplied to word lines WL4through WL6 connected with the second sub-block. The selection word lineVsw may be a low voltage.

A string selection line SSL may be floated from the point of time t1when the erase voltage Vers starts to be applied. A voltage of thestring selection line SSL may be increased by the coupling effect. Thestring selection transistor SST may be erase-inhibited.

At t2, the ground selection line GSL, the dummy word line DWL, and theword lines WL1 through WL3 of the first sub-block may be floated.Voltages of the ground selection line GSL, the dummy word line DWL, andthe word lines WL1 through WL3 may be increased due to the couplingeffect. The Fowler-Nordheim tunneling may not be generated at a groundselection transistor GST, a dummy memory cell DMC, and memory cells MC1through MC3 of the first sub-block. The ground selection transistor GST,the dummy memory cell DMC, and the memory cells MC1 through MC3 may beerase-inhibited.

After t2, the Fowler-Nordheim tunneling may be generated at memory cellsMC4 through MC6 of the second sub-block due to a difference between theerase voltage Vers and the selection word line voltage Vsw. Data of thememory cells MC4 through MC6 of the second sub-block may be erased.

FIG. 12 is a flowchart for describing a method of controlling word linesconnected with an unselected sub-block at an erase operation. Referringto FIGS. 1 and 12, in operation S110, an erase command may be received.Control logic 150 may receive a control signal CTRL provided as theerase command. Further, an address decoder 120 may receive an addressADDR appointing a sub-block to be erased. A sub-block corresponding tothe address ADDR may be a selected sub-block. A sub-block notcorresponding to the address ADDR may be an unselected sub-block.

In operation S120, there may be judged whether the unselected sub-blockis located between a substrate 111 and the selected sub-block. That is,there may be judged whether the unselected sub-block is disposed to becloser than the substrate 111 as compared with the selected sub-block.The control logic 150 may judge whether the unselected sub-block isdisposed to be closer than the substrate 111 as compared with theselected sub-block, based on the address ADDR.

In the event that the unselected sub-block is not located between thesubstrate 111 and the selected sub-block, the method proceeds tooperation S130. In the event that the unselected sub-block is locatedbetween the substrate 111 and the selected sub-block, the methodproceeds to operation S140.

In operation S130, word lines of the unselected sub-block may befloated. In an embodiment, a floating point of time may be equal to apoint of time when an erase voltage Vers is supplied to a substrate 111.

In operation S140, after a non-selection word line voltage Vusw issupplied to word lines of the unselected sub-block, the word lines ofthe unselected sub-block may be floated. The address decoder 120 maysupply the non-selection word line voltage Vusw to the word lines of theunselected sub-block. The address decoder 120 may float the word linesof the unselected sub-block after the erase voltage Vers is supplied anda specific delay time elapses. The control logic 150 may control a pointof time when the word lines of the unselected sub-block are floated.

With the embodiment described in relation to FIG. 12, a floating pointof time of word lines connected with the unselected sub-block may bedetermined according to a location of the unselected sub-block.

FIG. 13 is a timing diagram illustrating another embodiment of a voltagevariation of a memory block BLK1 according to a bias condition of FIG.10. It is assumed that a first sub-block is an unselected sub-block anda second sub-block is a selected sub-block.

Referring to FIGS. 9, 10, and 13, a ground selection line GSL, a dummyword line DWL, and word lines WL1 through WL3 of the first sub-block maybe floated at different points of time.

After receiving a ground selection line voltage Vgsl until t2, theground selection line GSL may be floated. After receiving a dummy wordline voltage Vdw until t3, the dummy word line DWL may be floated. Afterreceiving a non-selection word line voltage Vusw until t4, the wordlines WL1 through WL3 of the first sub-block may be floated. The time t3may follow the time t2, and the time t4 may follow the time t3. Thetimes t2 through t4 may be previously decided.

An erase voltage Vers supplied to a substrate 111 may be transferred toa surface layer 114 in a second direction. Between t1 and t2, the erasevoltage Vers of the substrate 111 may be stably transferred to a surfacelayer corresponding to a ground selection transistor GST by applying aground selection line voltage Vgsl to a ground selection line GSL.Between t2 and t3, the erase voltage Vers of a surface layercorresponding to the ground selection transistor GST may be stablytransferred to a surface layer corresponding to a dummy memory cell DMCby applying a dummy word line voltage Vdw to a dummy word line DWL.Between t3 and t4, the erase voltage Vers of a surface layercorresponding to the dummy memory cell DMC may be stably transferred toa surface layer corresponding to memory cells MC1 through MC3 of anunselected sub-block by applying a non-selection word line voltage Vusw.

As a result, the erase voltage Vers of the substrate 111 may beefficiently transferred to the surface layer 114 by sequentiallyfloating the ground selection line GSL, the dummy word line DWL, and theword lines WL1 through WL3 of the first sub-block.

FIG. 14 is a block diagram schematically illustrating a nonvolatilememory according to another embodiment of the inventive concept.Referring to FIG. 14, a nonvolatile memory 100 a of this exampleincludes a memory cell array 110, an address decoder 120, a voltagegenerator 130, a read and write circuit 140, control logic 150, and atime register 160.

The time register 160 may store time values. For example, the timevalues may be stored in the memory cell array 110. At power-up of thenonvolatile memory 110 a, the time values stored in the memory cellarray 110 may be loaded onto the time register 160.

The time register 160 may store a difference value between a first timet1 and a second time t2, a difference value between the second time t2and a third time t3, and a difference value between the third time t3and a fourth time t4.

The control logic 150 may judge floating points of time of a groundselection line GSL, a dummy word line DWL, and word lines WL1 throughWL3 of a first sub-block, based on the time values in the time register160, and may control the address decoder 120 according to a judgmentresult.

FIG. 15 is a timing diagram illustrating still another embodiment of avoltage variation of a memory block BLK1 according to a bias conditionof FIG. 10. It is assumed that a first sub-block is an unselectedsub-block and a second sub-block is a selected sub-block.

Referring to FIGS. 9, 10, and 15, floating points of time of a groundselection line GSL, a dummy word line DWL, and word lines WL1 throughWL3 of the first sub-block may be decided according to a level of anerase voltage Vers.

The ground selection line GSL may be floated when the erase voltage Versis over a first threshold voltage Vt1. The dummy word line DWL may befloated when the erase voltage Vers is over a second threshold voltageVt2. The word lines WL1 through WL3 of the unselected sub-block may befloated when the erase voltage Vers is over a third threshold voltageVt3. The first threshold voltage Vt1 may be lower than the secondthreshold voltage Vt2, and the second threshold voltage Vt2 may be lowerthan the third threshold voltage Vt3. The ground selection line GSL, thedummy word line DWL, and the word lines WL1 through WL3 of theunselected sub-block may be sequentially floated according to anincrease in the erase voltage Vers.

FIG. 16 is a block diagram schematically illustrating a nonvolatilememory according to still another embodiment of the inventive concept.Referring to FIG. 16, a nonvolatile memory 100 b of this exampleincludes a memory cell array 110, an address decoder 120, a voltagegenerator 130, a read and write circuit 140, control logic 150, and avoltage detector 170.

The voltage detector 170 may detect an erase voltage Vers supplied to asubstrate 111 of the nonvolatile memory 110 b. For example, the voltagedetector 170 may detect whether the erase voltage Vers reaches firstthrough third threshold voltages Vt1 through Vt3, respectively.

The control logic 150 may decide floating points of time of a groundselection line GSL, a dummy word line DWL, and word lines WL1 throughWL3 of an unselected sub-block, according to a detection result of thevoltage detector 170.

If the voltage detector 170 detects that the erase voltage Vers reachesthe first threshold voltage Vt1, the control logic 150 may control theaddress decoder 120 such that the ground selection line GSL is floated.If the voltage detector 170 detects that the erase voltage Vers reachesthe second threshold voltage Vt2, the control logic 150 may control theaddress decoder 120 such that the dummy word line DWL is floated. If thevoltage detector 170 detects that the erase voltage Vers reaches thethird threshold voltage Vt3, the control logic 150 may control theaddress decoder 120 such that the word lines WL1 through WL3 of anunselected sub-block are floated.

FIG. 17 is a diagram illustrating an embodiment in which memory cells MCof one NAND string NS11 are included within three sub-blocks. Referringto FIG. 17, a ground selection transistor GST, a dummy memory cell DMC,first through sixth memory cells MC1 through MC6, and a string selectiontransistor SST may be sequentially stacked on a substrate 111.

The memory cells MC1 and MC2 having third and fourth nominal heights maybe included within a first sub-block. The memory cells MC3 and MC4having fifth and sixth nominal heights may be included within a secondsub-block. The memory cells MC5 and MC6 having seventh and eighthnominal heights may be included within a third sub-block.

Like memory cells of the NAND string NS11, memory cells of the remainingNAND strings of a first memory block BLK1 may be included within thefirst through third sub-blocks. Accordingly, the first memory block BLK1may include three sub-blocks.

FIG. 18 is a table illustrating an embodiment of a bias condition in theevent that memory cells of a memory block BLK1 are included within threesub-blocks. Below, it is assumed that data of a second sub-block iserased. In this case, first and third sub-blocks may be unselected and asecond sub-block may be selected.

In accordance with an embodiment of FIG. 18, lines GSL, DWL, WL1, andWL2 connected with regions GST, DMC, MC1, and MC2 adjacent to asubstrate 111 than a selected sub-block may be floated after an erasevoltage Vers is applied and a specific delay time elapses. Lines WL5,WL6, and SSL connected with regions MC5, MC6, and SST far from thesubstrate than the selected sub-block may be floated when the erasevoltage Vers is supplied to the substrate 111.

Referring to FIGS. 7, 17, and 18, the erase voltage Vers is supplied tothe substrate 111.

When the erase voltage Vers is supplied, a selection word line voltageVsw may be applied to word lines WL3 and WL4 of the second sub-block.

Before a ground selection line GSL and a dummy word line DWL arefloated, a ground selection line voltage Vgsl and a dummy word linevoltage Vdw may be supplied to the ground selection line GSL and thedummy word line DWL, respectively. Before word lines WL1 and WL2 of thefirst sub-block are floated, a non-selection word line voltage Vusw maybe provided to the word lines WL1 and WL2 of the first sub-block.

Word lines WL5 and WL6 of the third sub-block and a string selectionline SSL may be floated.

FIG. 19 is a timing diagram illustrating a voltage variation of a memoryblock BLK1 according to a bias condition of FIG. 18. Referring to FIGS.17 through 19, at t1, an erase voltage may be supplied to a substrate111. Further, at t1, word lines WL5 and WL5 of a third sub-block and astring selection line SSL may be floated. Voltages of the word lines WL5and WL5 and the string selection line SSL may be increased due to thecoupling effect.

Between t1 and t2, a ground selection line voltage Vgsl and a dummy wordline voltage Vdw may be applied to a ground selection line GSL and adummy word line DWL, respectively. Also, a non-selection word linevoltage Vusw may be applied to word lines WL1 and WL2 of the firstsub-block, respectively.

The ground selection line voltage Vgsl, the dummy word line voltage Vdw,and the non-selection word line voltage Vusw may be a low voltage. Adifference between each of the voltages Vgsl, Vdw, and Vusw and theerase voltage Vers may be maintained. Accordingly, the erase voltageVers increasing may be stably transferred to a surface layercorresponding to memory cells MC3 and MC4 of the second sub-block.

A ground selection line GSL, a dummy word line DWL, and word lines WL1and WL2 of the first sub-block may be floated at t2. Voltages of theground selection line GSL, the dummy word line DWL, and the word linesWL1 and WL2 of the first sub-block may be increased due to the couplingeffect. A ground selection transistor GST, a dummy memory cell DMC, andmemory cells MC1 and MC2 of the first sub-block may be erase-inhibited.

FIG. 20 is a table illustrating another embodiment of a bias conditionin the event that memory cells of a memory block BLK1 are includedwithin three sub-blocks. An embodiment of FIG. 20 may be different fromthat of FIG. 18 in that lines WL5, WL6, and SSL connected with regionsMC5, MC6, and SST far from a substrate 111 than a selected sub-block arefloated after an erase voltage Vers is applied to the substrate 111 anda specific delay time elapses.

Referring to FIG. 20, a string selection line SSL and word lines WL5 andWL6 of a third sub-block may be floated after a specific delay time froma point of time when the erase voltage Vers is applied. After suppliedwith a string selection line voltage Vss1, the string selection line SSLmay be floated. After supplied with a non-selection word line voltageVusw, the word lines WL5 and WL6 of the third sub-block may be floated.

A plurality of bit lines BL1 through BLm may be connected to a pluralityof memory blocks BLK1 through BLKz (refer to FIG. 3). It is assumed thatthe plurality of memory blocks BLK1 through BLKz are disposed on onesubstrate 111. At this time, the erase voltage Vers supplied to thesubstrate 111 may be transferred to NAND strings of a first memory blockBLK1 via the bit lines BL1 through BLm and NAND strings of the remainingmemory blocks (e.g., BLKz).

The plurality of bit lines BL1 through BLm may be connected to aplurality of NAND strings (refer to FIGS. 3 and 7). The erase voltageVers supplied to the substrate 111 may be transferred to NAND stringsNS11 via other NAND strings (e.g., NS21 and NS31) and a bit line (e.g.,BL1).

With the embodiment of FIG. 20, the erase voltage Vers transferred via abit line may be stably transferred to a surface layer 114 by applyinglow voltages to a string selection line SSL and word lines WL5 and WL6of the third sub-block.

FIG. 21 is a table illustrating still another embodiment of a biascondition in the event that memory cells of a memory block BLK1 areincluded within three sub-blocks. An embodiment of FIG. 21 may bedifferent from that of FIG. 18 in that word lines WL5 and WL6 of a thirdsub-block are floated at different points of time.

Referring to FIG. 21, the fifth word line WL5 may be floated after aspecific delay time from a point of time when an erase voltage Vers isapplied. After supplied with a non-selection word line voltage Vuswafter a specific delay time, the fifth word line WL5 may be floated. Thesixth word line WL6 may be floated from a point of time when the erasevoltage Vers is applied.

It is assumed that the fifth word line WL5 is floated from a point oftime when the erase voltage Vers is applied. A voltage of the fifth wordline WL5 may be increased according to an increase in the erase voltageVers. The increased voltage of the fifth word line WL5 may affect anerase operation of a second sub-block. For example, the coupling betweenthe fifth word line WL5 and the second sub-block may become larger dueto the increased voltage of the fifth word line WL5.

With the embodiment of FIG. 21, a word line WL5 of a third sub-blockadjacent to a second sub-block may be supplied with a non-selection wordline voltage Vusw during a specific delay time. Word lines WL3 and WL4of a second sub-block may be supplied with a selection word line voltageVsw. The non-selection word line voltage Vusw and the selection wordline voltage Vsw may be a low voltage. For example, the non-selectionword line voltage Vusw and the selection word line voltage Vsw may be aground voltage. The coupling between the second sub-block and the thirdsub-block may be reduced by applying the non-selection word line voltageVusw to the word line WL5 adjacent to the second sub-block. Accordingly,the reliability of an erase operation on the second sub-block may bebettered.

In FIG. 21, there is illustrated the case that floating points of timeof the word lines WL5 and WL6 of the third sub-block are different.However, like the third sub-block, floating points of time of word linesWL1 and WL2 of a first sub-block can be controlled differently. Forexample, the second word line WL2 may be floated after a specific delaytime from a point of time when the erase voltage Vers is applied. Thefirst word line WL1 may be floated from a point of time when the erasevoltage Vers is applied.

FIG. 22 is a table illustrating still another embodiment of a biascondition in the event that memory cells of a memory block BLK1 areincluded within three sub-blocks. Referring to FIG. 22, after suppliedwith a non-selection word line voltage Vusw, word lines of unselectedsub-blocks (e.g., first and third sub-blocks) may be supplied with aspecific voltage.

The non-selection word line voltage Vusw may be applied to word linesWL1 and WL2 of the first sub-block. To prevent the Fowler-Nordheimtunneling, a first voltage V1 may be supplied to the word lines WL1 andWL2 of the first sub-block.

The non-selection word line voltage Vusw may be applied to word linesWL5 and WL6 of the third sub-block. To prevent the Fowler-Nordheimtunneling, a second voltage V2 may be supplied to the word lines WL5 andWL6 of the third sub-block.

In an embodiment, the first voltage V1 may be equal to voltages of theword lines WL1 and WL2 of the first sub-block when the word lines WL1and WL2 of the first sub-block are floated. The second voltage V2 may beequal to voltages of the word lines WL5 and WL6 of the third sub-blockwhen the word lines WL5 and WL6 of the third sub-block are floated.

FIG. 23 is a circuit diagram illustrating an equivalent circuit BLK1 cof one BLK1 of memory blocks BLK1 through BLKz according to anotherembodiment of the inventive concept. Referring to FIG. 23, one NANDstring may include a ground selection transistor GST, a first dummymemory cell DMC1, first through third memory cells MC1 through MC3, asecond dummy memory cell DMC2, fourth through sixth memory cells MC4through MC6, a third dummy memory cell DMC3, and a string selectiontransistor which are sequentially disposed from a substrate 111 (referto FIGS. 4 and 5).

In each NAND string, the first through third memory cells MC1 throughMC3 may constitute a first sub-block, and the fourth through sixthmemory cells MC4 through MC6 may constitute a second sub-block.

One NAND string may include three dummy memory cells DMC1, DMC2, andDMC3. The dummy memory cell DMC1 may be disposed between the groundselection transistor GST and the first sub-block, the dummy memory cellDMC2 between the first sub-block and the second sub-block, and the dummymemory cell DMC3 between the second sub-block and a string selectiontransistor SST.

FIG. 24 is a table illustrating a bias condition on an equivalentcircuit BLK1 c of FIG. 23 when a first sub-block is unselected and asecond sub-block is selected.

Referring to FIGS. 23 and 24, at an erase operation, an erase voltageVers may be supplied to a substrate 111 (refer to FIGS. 4 and 5), and aselection word line voltage Vsw may be supplied to word lines of asecond sub-block.

Lines GSL, DWL1, WL1 through WL3, and DWL2 connected to a regionadjacent to the substrate 111 than a selected sub-block may be floatedafter a specific delay time from a point of time when the erase voltageVers is supplied to the substrate 111.

Floating points of time of lines DWL3 and SSL connected to a region farfrom the substrate 111 than the selected sub-block may be decidedselectively. For example, the lines DWL3 and SSL connected to a regionfar from the substrate 111 than the selected sub-block may be floatedfrom a point of time when the erase voltage Vers is supplied to thesubstrate 111. Alternatively, the lines DWL3 and SSL connected to aregion far from the substrate 111 than the selected sub-block may befloated after a specific delay time from a point of time when the erasevoltage Vers is supplied to the substrate 111.

FIG. 25 is a table illustrating a bias condition on an equivalentcircuit BLK1 c of FIG. 23 when a first sub-block is selected and asecond sub-block is unselected.

Referring to FIGS. 23 and 25, at an erase operation, an erase voltageVers may be supplied to a substrate 111 (refer to FIGS. 4 and 5), and aselection word line voltage Vsw may be supplied to word lines of a firstsub-block.

Lines GSL and DWL1 connected to a region adjacent to the substrate 111than a selected sub-block may be floated after a specific delay timefrom a point of time when the erase voltage Vers is supplied to thesubstrate 111. Floating points of time of lines DWL2, WL4 through WL6,DWL3, and SSL connected to a region far from the substrate 111 than theselected sub-block may be decided selectively.

FIG. 26 is a block diagram illustrating a memory system according to anembodiment of the inventive concept. Referring to FIG. 26, a memorysystem 1000 may include a nonvolatile memory 100 and a controller 500.

The controller 500 may be coupled with a host and the nonvolatile memory100. The controller 500 may be configured to access the nonvolatilememory 100 in response to a request from the host. The controller 500may be configured to control read, program, erase, and backgroundoperations of the nonvolatile memory 100, for example. The controller500 may be configured to provide an interface between the nonvolatilememory 100 and the host. The controller 500 may be configured to drivefirmware for controlling the nonvolatile memory 100.

The controller 500 may include an internal bus 510, a processor 520, aRAM 530, a host interface 540, an ECC block 550, and a memory interface560. The internal bus 510 may provide a channel among constituentelements of the controller 500.

The processor 520 may control an overall operation of the controller500. For example, the processor 520 may be configured to drive firmware,code, and the like which are driven at the controller 500. For example,the processor 520 may be configured to drive firmware, code, and thelike which are used to control the nonvolatile memory 100.

The RAM 530 may be used as at least one of a working memory of theprocessor 530, a cache memory between the nonvolatile memory 100 and thehost or a buffer memory between the nonvolatile memory 100 and the host.

The host interface 540 may include the protocol for executing dataexchange between the host and the controller 500. Exemplarily, the hostinterface 540 may communicate with an external device (e.g., the host)via at least one of various protocols such as an USB (Universal SerialBus) protocol, an MMC (multimedia card) protocol, a PCI (peripheralcomponent interconnection) protocol, a PCI-E (PCI-express) protocol, anATA (Advanced Technology Attachment) protocol, a Serial-ATA protocol, aParallel-ATA protocol, a SCSI (small computer small interface) protocol,an ESDI (enhanced small disk interface) protocol, and an IDE (IntegratedDrive Electronics) protocol.

The ECC block 550 may include an Error Correcting Code (ECC).

The ECC block 550 may be configured to detect and correct an error ofdata read from the nonvolatile memory 100 using the ECC.

The memory interface 560 may interface with the nonvolatile memory 100.The memory interface 560 may include a NAND interface or a NORinterface, for example.

The controller 500 and the nonvolatile memory 100 may be integrated in asingle semiconductor device. The controller 500 and the nonvolatilememory 100 may be integrated in a single semiconductor device to form amemory card. For example, the controller 500 and the nonvolatile memorydevice 100 may be integrated in a single semiconductor device to form amemory card such as a PC (PCMCIA) card, a CF card, an SM (or, SMC) card,a memory stick, a multimedia card (MMC, RS-MMC, MMCmicro), a securitycard (SD, miniSD, microSD, SDHC), a universal flash storage (UFS)device, or the like.

The controller 500 and the nonvolatile memory 100 may be integrated in asingle semiconductor device to form a solid state drive (SSD). The SSDmay include a storage device configured to store data in a semiconductormemory. If the memory system 1000 is used as the SSD, it is possible tosubstantially improve an operating speed of a host coupled with thememory system 1000.

In some embodiments, the memory system 1000 may be used as computer,portable computer, Ultra Mobile PC (UMPC), workstation, net-book, PDA,web tablet, wireless phone, mobile phone, smart phone, e-book, PMP(portable multimedia player), digital camera, DMB (Digital MultimediaBroadcasting) player, digital audio recorder/player, digitalpicture/video recorder/player, portable game machine, navigation system,black box, 3-dimensional television, a device capable of transmittingand receiving information at a wireless circumstance, one of variouselectronic devices constituting home network, one of various electronicdevices constituting computer network, one of various electronic devicesconstituting telematics network, RFID, or one of various electronicdevices constituting a computing system.

In an exemplary embodiment, a nonvolatile memory 1100 or a memory system1000 may be packaged in accordance with a variety of packagetechnologies such as PoP (Package on Package), Ball grid arrays (BGAs),Chip scale packages (CSPs), Plastic Leaded Chip Carrier (PLCC), PlasticDual In-Line Package (PDIP), Die in Waffle Pack, Die in Wafer Form, ChipOn Board (COB), Ceramic Dual In-Line Package (CERDIP), Plastic MetricQuad Flat Pack (MQFP), Thin Quad Flatpack (TQFP), Small Outline (SOIC),Shrink Small Outline Package (SSOP), Thin Small Outline (TSOP), SystemIn Package (SIP), Multi Chip Package (MCP), Wafer-level FabricatedPackage (WFP), Wafer-Level Processed Stack Package (WSP), and the like.

FIG. 27 is a block diagram illustrating an application of a memorysystem in FIG. 26. Referring to FIG. 27, a memory system 2000 mayinclude a nonvolatile memory 2100 and a controller 2200. The nonvolatilememory 2100 may include a plurality of nonvolatile memory chips. Theplurality of nonvolatile memory chips may be classified into a pluralityof groups. Nonvolatile memory chips in each group may communicate withthe controller 2200 via a common channel In FIG. 27, there isillustrated the case that a plurality of memory chips communicates withthe controller 2200 via plural channels CH1 through CHk. Eachnonvolatile memory chip may be configured to operate the same as one ofnonvolatile memories 100 and 500 described in relation to FIGS. 1 and26.

As illustrated in FIG. 27, one channel may be connected with a pluralityof nonvolatile memory chips. However, the memory system 2000 may bemodified such that one channel is connected with one nonvolatile memorychip.

FIG. 28 is a block diagram illustrating a computing system including amemory system described in FIG. 27. Referring to FIG. 28, a computingsystem 3000 may include a CPU 3100, a RAM 3200, a user interface 3300, apower supply 3400, and a memory system 2000.

The memory system 2000 may be electrically connected with the CPU 3100,the RAM 3200, the user interface 3300, and the power supply 3400 via asystem bus 3500. Data provided via the user interface 3300 or processedby the CPU 3100 may be stored in the memory system 2000.

As illustrated in FIG. 28, a nonvolatile memory 2100 may be connectedwith a system bus 3500 via a controller 2200. However, the nonvolatilememory 2100 can be connected directly with the system bus 3500. At thistime, a function of the controller 2200 may be executed by the CPU 3100.

The memory system 2000 in FIG. 28 may be a memory system described inrelation to FIG. 27. However, the memory system 2000 can be replacedwith a memory system 1000 described in relation to FIG. 26. In anembodiment, the computing system 3000 may be configured to include allmemory systems 1000 and 2000 described in relation to FIGS. 26 and 27.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope. Thus, to the maximum extent allowed by law,the scope is to be determined by the broadest permissible interpretationof the following claims and their equivalents, and shall not berestricted or limited by the foregoing detailed description.

What is claimed is:
 1. A method of erasing a nonvolatile memory devicewhich includes a plurality of memory cell strings including a firstmemory cell string, the first memory cell string including a firstground selection transistor, a plurality of nonvolatile memory cells anda first dummy memory cell, the first ground selection transistor beingconnected to a source line, and the plurality of memory cells and thefirst dummy memory cell being stacked on or above a substrate in adirection that is perpendicular to the substrate, the method comprising:generating an erase voltage that begins to rise at a first time point,the erase voltage being supplied to a channel of the first memory cellstring; supplying a first voltage to a ground selection line connectedto the first ground selection transistor and a second voltage to a firstdummy word line connected to the first dummy memory cell while the erasevoltage rises from the first time point; then floating the groundselection line at a second time point that is later than the first timepoint; and floating the first dummy word line at a third time point thatis later than the second time point.
 2. The method of claim 1, whereinbetween the first time point and the third time point, the erase voltagecontinues to rise, the first voltage is supplied to the ground selectionline between the first time point and the second time point, and thesecond voltage is supplied to the first dummy word line between thefirst time point and the third time point.
 3. The method of claim 2,wherein the first dummy memory cell is disposed between the first groundselection transistor and the plurality of nonvolatile memory cells. 4.The method of claim 3, further comprising supplying a plurality of thirdvoltages to a plurality of word line connected to the plurality ofmemory cells respectively during the erase voltage being supplied to thechannel of the first memory cell string.
 5. The method of claim 1,wherein a level of the first voltage and a level of the second voltageare equal to a level of a ground voltage.
 6. The method of claim 4,wherein the erase voltage is maintained at a target level from a fourthtime point that is later than the third time point.
 7. The method ofclaim 6, further comprising floating a second dummy word line at thethird time point, the second dummy word line being connected to a seconddummy memory cell that is included in the first memory cell string. 8.The method of claim 6, further comprising floating a second dummy wordline after the second time point, the second dummy word line beingconnected to a second dummy memory cell that is included in the firstmemory cell string.
 9. The method of claim 7, wherein the first memorycell string is connected to a first bit-line, the plurality of memorycell strings includes a second memory cell string that is connected tothe first bit-line, and a second ground selection transistor included inthe second memory cell string is connected to the ground selection line.10. A method of erasing a nonvolatile memory device which includes aplurality of memory cell strings including a first memory cell string,the first memory cell string including a first ground selectiontransistor, a plurality of nonvolatile memory cells and a first dummymemory cell, the first ground selection transistor being connected to asource line, and the plurality of memory cells and the first dummymemory cell being stacked on or above a substrate in a direction that isperpendicular to the substrate, the method comprising: supplying anerase voltage that begins to rise at a first time point to thesubstrate; supplying a first voltage to a ground selection lineconnected to the first ground selection transistor and a second voltageto a first dummy word line connected to the first dummy memory cellwhile the erase voltage rises from the first time point; floating theground selection line at a second time point that is later than thefirst time point; and floating the dummy word line at a third time pointthat is later than the second time point.
 11. The method of claim 10,wherein between the first time point and the third time point, the erasevoltage continues to rise, the first voltage is supplied to the groundselection line between the first time point and the second time point,and the second voltage is supplied to the first dummy word line betweenthe first time point and the third time point.
 12. The method of claim11, wherein the first dummy memory cell is disposed between the firstground selection transistor and the plurality of nonvolatile memorycells.
 13. The method of claim 12, further comprising supplying aplurality of third voltages to a plurality of word line connected to theplurality of memory cells respectively during the erase voltage beingsupplied to the channel of the first memory cell string.
 14. The methodof claim 10, wherein a level of the first voltage and a level of thesecond voltage are equal to a level of a ground voltage.
 15. The methodof claim 13, wherein the erase voltage is maintained at a target levelfrom a fourth time point that is later than the third time point. 16.The method of claim 15, further comprising floating a second dummy wordline at the third time point, the second dummy word line being connectedto a second dummy memory cell that is included in the first memory cellstring.
 17. The method of claim 15, further comprising floating a seconddummy word line after the second time point, the second dummy word linebeing connected to a second dummy memory cell that is included in thefirst memory cell string.
 18. The method of claim 16, wherein the firstmemory cell string is connected to a first bit-line, the plurality ofmemory cell strings includes a second memory cell string that isconnected to the first bit-line, and a second ground selectiontransistor included in the second memory cell string is connected to theground selection line.
 19. A nonvolatile memory device comprising: amemory cell array including a plurality of memory cell strings includinga first memory cell string, the first memory cell string including afirst ground selection transistor, a plurality of nonvolatile memorycells and a first dummy memory cell, the first ground selectiontransistor being connected to a source line, and the plurality of memorycells and the first dummy memory cell being stacked on or above asubstrate in a direction that is perpendicular to the substrate; avoltage generator configured to generate an erase voltage supplied to achannel of the first memory cell string, the erase voltage rising from afirst level; an address decoder configured to supply a first voltage toa ground selection line connected to the first ground selectiontransistor and a second voltage to a first dummy word line connected tothe first dummy memory cell; a time register configured to store a firstand a second time values; and a control logic configured to determine afirst time point of floating the ground selection line based on thefirst time value and to determine a second time point of floating thedummy word line based on the second time value, configured to generateone or more control signals based on the first time point and the secondtime point, and configured to send the one or more control signals tothe address decoder, wherein the address decoder is configured to floatthe ground selection line and the dummy word line in response to the oneor more control signals while the erase voltage rises from the firstlevel, and the second time point is later than the first time point. 20.The nonvolatile memory device of claim 19, wherein between the firsttime point and the third time point, the erase voltage continues torise, the first voltage is supplied to the ground selection line betweenthe first time point and the second time point, and the second voltageis supplied to the first dummy word line between the first time pointand the third time point.
 21. The nonvolatile memory device of claim 20,wherein the first dummy memory cell is disposed between the first groundselection transistor and the plurality of nonvolatile memory cells. 22.The nonvolatile memory device of claim 21, wherein the address decoderconfigured to supply a plurality of third voltages to a plurality ofword line connected to the plurality of memory cells respectively duringthe erase voltage being supplied to the channel of the first memory cellstring.
 23. The nonvolatile memory device of claim 22, wherein the erasevoltage is maintained at a target level from a fourth time point that islater than the third time point.
 24. The nonvolatile memory device ofclaim 23, the address decoder configured to float a second dummy wordline after the second time point, the second dummy word line beingconnected to a second dummy memory cell that is included in the firstmemory cell string.
 25. The nonvolatile memory device of claim 24,wherein the first memory cell string is connected to a first bit-line,the plurality of memory cell strings includes a second memory cellstring that is connected to the first bit-line, and a second groundselection transistor included in the second memory cell string isconnected to the ground selection line.
 26. A memory system comprising:a memory controller configured to provide a erase command and anaddress; and a memory cell array comprising a plurality of memory cellstrings including a first memory cell string, the first memory cellstring including a first ground selection transistor, a plurality ofnonvolatile memory cells, a first dummy memory cell that is disposedbetween the first ground selection transistor and the plurality ofnonvolatile memory cells and a second dummy memory cell, the firstground selection transistor being connected to a source line, and theplurality of memory cells, the first dummy memory cell and the seconddummy memory cell being connected in series and stacked on or above asubstrate in a direction that is perpendicular to the substrate, avoltage generator configured to generate an erase voltage in response tothe erase command, the erase voltage being supplied to a channel of thefirst memory cell string corresponding to the address, the erase voltagerising from a first level; an address decoder configured to supply afirst voltage to a ground selection line connected to the first groundselection transistor, to supply a second voltage to a first dummy wordline connected to the first dummy memory cell and to supply a pluralityof third voltages to a plurality of word lines connected to theplurality of memory cells respectively; a time register configured tostore a first and a second time values; and a control logic configuredto determine a first time point of floating the ground selection linebased on the first time value and to determine a second time point offloating the dummy word line based on the second time value, configuredto generate one or more control signals based on the first time pointand the second time point, and configured to send the one or morecontrol signals to the address decoder, wherein the address decoder isconfigured to float the ground selection line and the dummy word line inresponse to the one or more control signals while the erase voltagerises from the first level, and the second time point is later than thefirst time point.
 27. The memory system of claim 26, wherein between thefirst time point and the third time point, the erase voltage continuesto rise, the first voltage is supplied to the ground selection linebetween the first time point and the second time point, and the secondvoltage is supplied to the first dummy word line between the first timepoint and the third time point.
 28. The memory system of claim 27,wherein the first memory cell string is connected to a first bit-line,the plurality of memory cell strings includes a second memory cellstring that is connected to the first bit-line, and a second groundselection transistor included in the second memory cell string isconnected to the ground selection line.
 29. The memory system of claim28, the address decoder configured to float a second dummy word lineafter the second time point, the second dummy word line being connectedto the second dummy memory cell.
 30. The memory system of claim 29,wherein the erase voltage is maintained at a target level from a fourthtime point that is later than the third time point.